U.S. patent application number 12/129434 was filed with the patent office on 2009-12-03 for silicon nanoparticle embedded insulating film photodetector.
Invention is credited to Pooran Chandra Joshi, Apostolos T. Voutsas, Hao Zhang.
Application Number | 20090294885 12/129434 |
Document ID | / |
Family ID | 41378722 |
Filed Date | 2009-12-03 |
United States Patent
Application |
20090294885 |
Kind Code |
A1 |
Joshi; Pooran Chandra ; et
al. |
December 3, 2009 |
Silicon Nanoparticle Embedded Insulating Film Photodetector
Abstract
A photodetector is provided with a method for fabricating a
semiconductor nanoparticle embedded Si insulating film for
photo-detection applications. The method provides a bottom
electrode and introduces a semiconductor precursor and hydrogen. A
thin-film is deposited overlying the substrate, using a high
density (HD) plasma-enhanced chemical vapor deposition (PECVD)
process. As a result, a semiconductor nanoparticle embedded Si
insulating film is formed, where the Si insulating film includes
either N or C elements. For example, the Si insulating film may be
a non-stoichiometric SiO.sub.XN.sub.Y thin-film, where (X+Y<2
and Y>0), or SiC.sub.X, where X<1. The semiconductor
nanoparticles are either Si or Ge. Following the formation of the
semiconductor nanoparticle embedded Si insulating film, an
annealing process is performed.
Inventors: |
Joshi; Pooran Chandra;
(Vancouver, WA) ; Zhang; Hao; (Vancouver, WA)
; Voutsas; Apostolos T.; (Portland, OR) |
Correspondence
Address: |
SHARP LABORATORIES OF AMERICA, INC.;C/O LAW OFFICE OF GERALD MALISZEWSKI
P.O. BOX 270829
SAN DIEGO
CA
92198-2829
US
|
Family ID: |
41378722 |
Appl. No.: |
12/129434 |
Filed: |
May 29, 2008 |
Current U.S.
Class: |
257/432 ;
257/E21.001; 257/E31.001; 438/63 |
Current CPC
Class: |
H01L 31/1804 20130101;
Y02E 10/547 20130101; Y02P 70/50 20151101; C23C 16/505 20130101;
C23C 16/308 20130101; H01L 31/0352 20130101; H01L 31/1085
20130101 |
Class at
Publication: |
257/432 ; 438/63;
257/E31.001; 257/E21.001 |
International
Class: |
H01L 31/00 20060101
H01L031/00; H01L 21/00 20060101 H01L021/00 |
Claims
1. A photodetector employing a semiconductor nanoparticle embedded
insulating film, the photodetector comprising: a bottom electrode;
a semiconductor nanoparticle embedded Si insulating film overlying
the bottom electrode, the insulating film including an element
selected from a group consisting of N and C; and, a transparent
electrode overlying the insulating film.
2. The photodetector of claim 1 wherein the Si insulating film is a
non-stoichiometric SiO.sub.X1N.sub.Y1 thin-film overlying the
bottom electrode, where (X1+Y1<2 and Y1>0).
3. The photodetector of claim 1 wherein the Si insulating film is a
SiC.sub.X thin film, where X<1.
4. The photodetector of claim 1 wherein the semiconductor
nanoparticles embedded in the Si insulating film have a diameter in
a range of about 1 to 10 nanometers (nm).
5. The photodetector of claim 1 wherein the semiconductor
nanoparticles are a material selected from a group consisting of Si
and Ge.
6. The photodetector of claim 1 wherein the bottom electrode is a
material selected from a group consisting of a doped semiconductor,
metal, and polymer.
7. The photodetector of claim 1 wherein the semiconductor
nanoparticle embedded Si insulating film exhibits a spectral
response in a wavelength range of about 200 nanometers (nm) to
about 1600 nm.
8. A method for fabricating a semiconductor nanoparticle embedded
Si insulating film for photo-detection applications, the method
comprising: providing a bottom electrode; introducing a
semiconductor precursor and hydrogen; depositing a thin-film
overlying the substrate, using a high density (HD) plasma-enhanced
chemical vapor deposition (PECVD) process; and, forming a
semiconductor nanoparticle embedded Si insulating film including an
element selected from a group consisting of N and C.
9. The method of claim 8 wherein the semiconductor nanoparticle
embedded Si insulating film is a non-stoichiometric
SiO.sub.XN.sub.Y thin-film, where (X+Y<2 and Y>0).
10. The method of claim 8 wherein the semiconductor nanoparticle
embedded Si insulating film is SiC.sub.X, where X<1.
11. The method of claim 8 wherein the semiconductor nanoparticles
are a material selected from a group consisting of Si and Ge.
12. The method of claim 8 wherein depositing the thin film using an
HD PECVD process includes using an inductively coupled plasma (ICP)
source.
13. The method of claim 8 further comprising: heating the substrate
to a temperature of less than about 400.degree. C.
14. The method of claim 8 wherein introducing the semiconductor
precursor and hydrogen includes supplying a precursor selected from
a group consisting of Si.sub.nH2.sub.n+2 and Ge.sub.nH.sub.2n+2,
where n varies from 1 to 4, SiH.sub.xR.sub.4-x where R is selected
from a first group consisting of Cl, Br, and I, and where x varies
from 0 to 3, and GeH.sub.xR.sub.4-x where R is selected from the
first group, and x varies from 0 to 3.
15. The method of claim 8 wherein depositing the thin-film using
the HD PECVD process includes using a plasma concentration of
greater than 1.times.10.sup.11 cm.sup.-3, with an electron
temperature of less than 10 eV.
16. The method of claim 8 wherein introducing the semiconductor
precursor and hydrogen includes: supplying power to a top electrode
at a frequency in the range of 13.56 to 300 megahertz (MHz), and a
power density of less than 10 watts per square centimeter
(W/cm.sup.2); supplying power to a bottom electrode at a frequency
in the range of 50 kilohertz to 13.56 MHz, and a power density of
up to 3 W/cm.sup.2; using an atmosphere pressure in the range of 1
to 500 mTorr; and, supplying an oxygen source gas; and, wherein
forming the semiconductor nanoparticle embedded Si insulating film
includes forming a SiO.sub.XN.sub.Y thin-film.
17. The method of claim 16 wherein supplying the oxygen source gas
includes supplying an oxygen source gas selected from a group
consisting of N.sub.2O, NO, O.sub.2, and O.sub.3.
18. The method of claim 17 wherein introducing the semiconductor
precursor and hydrogen includes supplying an inert noble gas.
19. The method of claim 16 wherein introducing the semiconductor
precursor and hydrogen includes supplying a nitrogen source gas,
selected from a group consisting of N.sub.2 and NH.sub.3.
20. The method of claim 8 further comprising: following the
formation of the semiconductor nanoparticle embedded Si insulating
film, annealing as follows: heating the substrate to a temperature
of greater than about 400.degree. C.; heating for a time duration
in the range of about 10 to 300 minutes; heating in an atmosphere
selected from a group consisting of oxygen and hydrogen, and
oxygen, hydrogen, and inert gases; and, modifying the size of the
semiconductor nanoparticles in the Si insulating film in response
to the annealing.
21. The method of claim 8 further comprising: following the
formation of the semiconductor nanoparticle embedded Si insulating
film, annealing using a heat source having a radiation wavelength
selected from a group consisting of about 150 to 600 nanometers
(nm) and 9 to 11 micrometers.
22. The method of claim 8 further comprising: performing a HD
plasma treatment with the semiconductor nanoparticle embedded Si
insulating film in an H.sub.2 atmosphere, using a substrate
temperature of less than 400.degree. C.; and, hydrogenating the
semiconductor nanoparticle embedded Si insulating film.
23. The method of claim 22 wherein hydrogenating the semiconductor
nanoparticle embedded Si insulating film using the HD plasma
process includes: supplying power to a top electrode at a frequency
in the range of 13.56 to 300 MHz, and a power density of up to 10
W/cm.sup.2; supplying power to a bottom electrode at a frequency in
the range of 50 kilohertz to 13.56 MHz, and a power density of up
to 3 W/cm.sup.2; using an atmosphere pressure in the range of 1 to
500 mTorr; and, supplying H.sub.2 and an inert gas.
24. The method of claim 8 further comprising: doping the
semiconductor nanoparticle embedded Si insulating film with a
dopant selected from a group consisting of Type 3, Type 4, Type 5,
and rare earth elements; and, in response to doping, forming a
semiconductor nanoparticle embedded Si insulating film with optical
absorption characteristics in a range of frequencies from deep
ultraviolet (UV) to far infrared (IR).
25. The method of claim 9 further comprising: following the
formation of the SiO.sub.XN.sub.Y thin-film, oxidizing the
non-stoichiometric SiO.sub.XN.sub.Y thin-film using a process
selected from a group consisting of plasma and thermal oxidation;
and, modifying the size of semiconductor nanoparticles in the
SiO.sub.XN.sub.Y thin-film in response to the oxidation
process.
26. The method of claim 9 wherein forming the SiO.sub.XN.sub.Y
thin-film includes forming a non-stoichiometric SiO.sub.XN.sub.Y
thin-film with values of X and Y that vary with respect to the
thickness of the thin-film.
27. The method of claim 8 wherein depositing the thin film includes
using the HD PECVD process includes: supplying power to a top
electrode at a frequency in the range of 13.56 to 300 MHz, and a
power density of less than 10 W/Cm.sup.2; supplying power to a
bottom electrode at a frequency in the range of 50 kilohertz to
13.56 MHz, and a power density of up to 3 W/cm.sup.2; using an
atmosphere pressure in the range of 1 to 500 mTorr; and, supplying
Si.sub.nH.sub.2n+2 and a C source; and, wherein forming the
semiconductor nanoparticle embedded Si insulating film includes
forming a SiC.sub.X thin-film.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] This invention generally relates to the fabrication of
integrated circuit (IC) photodetectors, and more particularly, to a
photodetector made from a silicon (Si) nanoparticle embedded
insulating film, using a high-density plasma-enhanced chemical
vapor deposition process.
[0003] 2. Description of the Related Art
[0004] The fabrication of integrated optical devices involves the
deposition of materials with suitable optical characteristics such
as absorption, transmission, and spectral response. Thin-film
fabrication techniques can produce diverse optical thin films,
which are suitable for the production of large area devices at high
throughput and yield. Some optical parameters of importance include
refractive index and the optical band-gap, which dictate the
transmission and reflection characteristics of the thin film.
[0005] Typically, bilayer or multilayer stack thin-films are
required for the fabrication of optical devices with the desired
optical effect. Various combinations of the metal, dielectric,
and/or semiconductor layers are also used to form multilayer films
with the desired optical characteristics. The selection of the
material depends on the target reflection, transmission, and
absorption characteristics. While a single layer device would
obviously be more desirable, no single thin-film material has been
able to provide the wide range of optical dispersion
characteristics required to get the desired optical absorption,
band-gap, refractive index, reflection, or transmission over a wide
optical range extending from ultraviolet (UV) to far infrared (IR)
frequencies.
[0006] Silicon is the material of choice for the fabrication of
optoelectronic devices because of well-developed processing
technology. However, the indirect band-gap makes it an inefficient
material for optoelectronic devices. Over the years, various
R&D efforts have focused on tailoring the optical function of
Si to realize Si-based optoelectronics. The achievement of
efficient room temperature light emission from the crystalline
silicon is a major step towards the achievement of fully Si-based
optoelectronics.
[0007] At present, the Si thin film-based photodetectors operating
at wavelengths shorter than 850 nm are attractive for low cost,
highly integrated CMOS devices. Si is an indirect bandgap
semiconductor with limited speed-responsivity performance, but it
is still useful for detection in UV-VIS (visible)-NIR (near-IR)
spectrum. However, the indirect bandgap of Si limits the critical
wavelength of Si to 1.12 .mu.m, beyond which its absorption goes to
zero, making it insensitive to two primary telecommunication
wavelengths of 1.30 and 1.55 .mu.m. An additional issue with Si
based photo-detectors is the dark current limiting the
signal-to-noise ratio (SNR), and the thermal instability at
operating temperatures higher than 50.degree. C.
[0008] The fabrication of stable and reliable optoelectronic
devices requires Si nanocrystals with high photoluminescence (PL)
and electroluminescence (EL) quantum efficiency. One approach that
is being actively pursued for integrated optoelectronic devices is
the fabrication of SiO.sub.x (x.ltoreq.2) thin films with embedded
Si nanocrystals. The luminescence due to recombination of the
electron-hole pairs confined in Si nanocrystals depends strongly on
the nanocrystal size. The electrical and optical properties of the
nanocrystalline Si embedded SiO.sub.xN.sub.y thin films depend on
the size, concentration, and distribution of the Si nanocrystals.
Various thin-film deposition techniques such as sputtering and
plasma-enhanced chemical vapor deposition (PECVD), employing a
capacitively-coupled plasma source, are being investigated for the
fabrication of stable and reliable nanocrystalline Si thin films,
which are also referred to herein as nanocrystalline Si embedded
insulating thin films.
[0009] However, conventional PECVD and sputtering techniques have
the limitations of low plasma density, inefficient power coupling
to the plasma, low ion/neutral ratio, and uncontrolled bulk, and
interface damage due to high ion bombardment energy. Therefore, the
oxide films formed from a conventional capacitively-coupled plasma
(CCP) generated plasma may create reliability issues due to the
high bombardment energy of the impinging ionic species. It is
important to control or minimize any plasma-induced bulk or
interface damage. However, it is not possible to efficiently
control the ion energy using the radio frequency (RF) power of CCP
generated plasma. Any attempt to enhance the reaction kinetics by
increasing the applied power results in increased bombardment of
the deposited film, creating a poor quality films with a high
defect concentration. Additionally, the low plasma density
associated with these types of sources
(.about.1.times.10.sup.8-10.sup.9 cm.sup.-3) leads to limited
reaction possibilities in the plasma and on the film surface,
inefficient generation of active radicals and ions for enhanced
process kinetics, inefficient oxidation, and process and system
induced impurities, which limits their usefulness in the
fabrication of low-temperature electronic devices.
[0010] A deposition process that offers a more extended processing
range and enhanced plasma characteristics than conventional
plasma-based techniques, such as sputtering, PECVD, etc., is
required to generate and control the particle size for PL and
electroluminescent (EL) based device development. A process that
can enhance plasma density and minimize plasma bombardment will
ensure the growth of high quality films without plasma-induced
microstructural damage. A process that can offer the possibility of
controlling the interface and bulk quality of the films
independently will enable the fabrication of high performance and
high reliability electronic devices. A plasma process that can
efficiently generate the active plasma species, radicals and ions,
will enable noble thin film development with controlled process and
property control.
[0011] For the fabrication of high quality SiOx thin films, the
oxidation of a grown film is also critical to ensure high quality
insulating layer across the nanocrystalline Si particles. A process
that can generate active oxygen radicals at high concentrations
will ensure the effective passivation of the Si nanoparticles
(nc-Si) in the surrounding oxide matrix. A plasma process that can
minimize plasma-induced damage will enable the formation of a high
quality interface that is critical for the fabrication of high
quality devices. Low thermal budget efficient oxidation and
hydrogenation processes are critical and will be significant for
the processing of high quality optoelectronic devices. The higher
temperature thermal processes can interfere with the other device
layers and they are not suitable in terms of efficiency and thermal
budget, due to the lower reactivity of the thermally activated
species. Additionally, a plasma process which can provide a more
complete solution and capability in terms of growth/deposition of
novel film structures, oxidation, hydrogenation, particle size
creation and control, and independent control of plasma density and
ion energy, and large area processing is desired for the
development of high performance optoelectronic devices. Also, it is
important to correlate the plasma process with the thin film
properties as the various plasma parameters dictate the thin film
properties and the desired film quality depends on the target
application. Some of the key plasma and thin-film characteristics
that depend on the target application are deposition rate,
substrate temperature, thermal budget, density, microstructure,
interface quality, impurities, plasma-induced damage, state of the
plasma generated active species (radicals/ions), plasma potential,
process and system scaling, and electrical quality and reliability.
A correlation among these parameters is critical to evaluate the
film quality as the process map will dictate the film quality for
the target application. It may not be possible to learn or develop
thin-films by just extending the processes developed in low density
plasma or other high-density plasma systems, as the plasma energy,
composition (radical to ions), plasma potential, electron
temperature, and thermal conditions correlate differently depending
on the process map.
[0012] Low temperatures are generally desirable in liquid crystal
display (LCD) manufacture, where large-scale devices are formed on
transparent glass, quartz, or plastic substrate. These transparent
substrates can be damaged when exposed to temperatures exceeding
650 degrees C. To address this temperature issue, low-temperature
Si oxidation processes have been developed. These processes use a
high-density plasma source such as an inductively coupled plasma
(ICP) source, and are able to form Si oxide with a quality
comparable to 1200 degree C. thermal oxidation methods.
[0013] It would be advantageous if the benefits realized with
high-density plasma Si-containing films could be used in the
fabrication of photodetectors made from semiconductor nanoparticle
embedded Si insulating films. As used herein, a Si insulating film
is an insulating film with Si as one of the constituent
elements.
SUMMARY OF THE INVENTION
[0014] The present invention describes a photodetector made from
semiconductor nanoparticles (e.g., nc-Si) embedded Si insulating
films, such as SiO.sub.xN.sub.y thin films. The nc-semiconductor
particles embedded in the insulating matrix generate high
photo-current at low reverse biases. The high SNR of the
nc-semiconductor embedded Si insulating thin films overcome the
limitations of conventional Si and wide-band gap
semiconductor-based photodetectors. The photoconduction in the
nc-semiconductor embedded Si insulating thin films makes possible
metal-film-metal (MFM) photodetectors, which offer the unique
advantages of high sensitivity-bandwidth product, low capacitance,
and ease of integration. The photo-response and the current
conduction in nc-semiconductor embedded Si insulating thin films
can be controlled over a broad range by varying the particle size
and distribution, particle density, inter-particle distance,
optical dispersion, and film composition. In fabricating the
semiconductor nanoparticles embedded Si insulating films, a low
temperature, high density plasma (HDP)-based process is
described.
[0015] Accordingly, a method is provided for fabricating a
semiconductor nanoparticle embedded Si insulating film for
photo-detection applications. The method provides a bottom
electrode and introduces a semiconductor precursor and hydrogen. A
thin-film is deposited overlying the substrate, using a high
density (HD) plasma-enhanced chemical vapor deposition (PECVD)
process. As a result, a semiconductor nanoparticle embedded Si
insulating film is formed, where the Si insulating film includes
either N or C elements. For example, the Si insulating film may be
a non-stoichiometric SiO.sub.XN.sub.y thin-film, where (X+Y<2
and Y>0), or SiC.sub.X, where X<1. The semiconductor
nanoparticles are either Si or Ge.
[0016] In one aspect, the method heats the substrate to a
temperature of less than about 400.degree. C., and the thin-film HD
PECVD process uses a plasma concentration of greater than
1.times.10.sup.11 cm.sup.-3, with an electron temperature of less
than 10 eV. Following the formation of the semiconductor
nanoparticle embedded Si insulating film, an annealing process is
performed. In one aspect, a heat source is used having a radiation
wavelength of about 200 to 600 nanometers (nm) or 9 to 11
micrometers. In another aspect, an HD plasma treatment is performed
in an H.sub.2 atmosphere, using a substrate temperature of less
than 400.degree. C., hydrogenating the semiconductor nanoparticle
embedded Si insulating film.
[0017] Additional details of the above-described method and a
photodetector employing a semiconductor nanoparticle embedded
insulating film are presented below.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] FIG. 1 is a partial cross-sectional view of a photodetector
employing a semiconductor nanoparticle embedded insulating
film.
[0019] FIG. 2 is a schematic block diagram depicting the
photodetector of FIG. 1 under bias, in a horizontal
configuration.
[0020] FIG. 3 is a schematic block diagram depicting the
photodetector of Fig. under bias, in a vertical configuration.
[0021] FIG. 4 is a schematic drawing of a high-density plasma (HDP)
system with an inductively coupled plasma source.
[0022] FIG. 5 depicts a setup used for photo-response
measurements.
[0023] FIG. 6 is a graph depicting photo-conduction characteristics
of a 200 nm-thick film deposited on an n.sup.+ silicon
substrate.
[0024] FIGS. 7A and 7B are graphs depicting the effect of the film
thickness and Si substrate doping on the photo-response
measurements.
[0025] FIGS. 8A and 8B are graphs depicting the effect of
temperature on current using films deposited on an n.sup.+
substrate.
[0026] FIG. 9A is a graph depicting SNR for a 50 nm-thick film
deposited on an n.sup.+ silicon substrate.
[0027] FIGS. 9B and 9C illustrate some optical dispersion
characteristics of nc-Si embedded SiO.sub.x thin films.
[0028] FIGS. 10A through 10C illustrate the PL spectrum of some HDP
processed nc-Si embedded SiO.sub.x thin films covering the visible
part of the spectrum.
[0029] FIG. 11 is a flowchart illustrating a method for fabricating
a semiconductor nanoparticle embedded Si insulating film for
photo-detection applications.
DETAILED DESCRIPTION
[0030] FIG. 1 is a partial cross-sectional view of a photodetector
employing a semiconductor nanoparticle embedded insulating film.
The photodetector 100 comprises a bottom electrode 102, which may
be a doped semiconductor, metal, or polymer. A semiconductor
nanoparticle embedded Si insulating film 104 overlies the bottom
electrode 102. The insulating film includes either N or C elements.
In one aspect, the Si insulating film 104 is a non-stoichiometric
SiO.sub.X1N.sub.Y1 thin-film, where (X1+Y1<2 and Y1>0). In
another aspect, the Si insulating film 104 is a SiC.sub.X thin
film, where X<1.
[0031] The semiconductor nanoparticles embedded in the Si
insulating film 104 have a diameter in the range of about 1 to 10
nanometers (nm), and are made from either Si or Ge. The
semiconductor nanoparticle embedded Si insulating film 104 exhibits
a spectral response in a wavelength range of about 200 nanometers
(nm) to about 1600 nm. A transparent electrode 106, such an indium
tin oxide (ITO) or a thin metal, overlies the insulating film.
[0032] The photo-conduction in nc-semiconductor embedded Si
insulator thin films overcomes the major limitations of Si and wide
hand gap (WBG) semiconductor-based photo-detectors, using charge
generation and conduction by the nc-semiconductor particles in a
dielectric matrix. The enhanced performance is due to various
control variables which are not available with Si or WBG
semiconductor-based photodetector (PD) devices whose
characteristics are dominantly defined by the material
characteristics.
[0033] The photodetector performance, spectral-response, and the
electrical conduction of the nc-semiconductor embedded Si
insulating thin films can be tuned over a wide range by varying the
particle size and distribution, particle density, inter-particle
distance, optical dispersion, film composition, and doping. The HDP
technique is suitable for the fabrication of high performance thin
films at low temperatures due to enhanced plasma characteristics
(high plasma density, low plasma potential, and independent control
of ion energy and density) compared to conventional plasma based
techniques. The present invention describes a method for creating
uniform particle distribution across the film thickness,
irrespective of the thickness, which is not achievable by other
approaches for nc-semiconductor particle formation such as ion
implantation. While it is difficult to quantify uniform particle
distribution effectively, the uniformity of distribution is a clear
advantage associated with the in-situ creation of nc-Si particles,
as compared to the Si ion implantation approach for nc-Si creation
in an insulating matrix.
[0034] FIG. 2 is a schematic block diagram depicting the
photodetector of FIG. 1 under bias, in a horizontal
configuration.
[0035] FIG. 3 is a schematic block diagram depicting the
photodetector of Fig. under bias, in a vertical configuration. The
carrier generation and conduction from particle-to-particle through
the insulating matrix permits controlled spectral responses and
electrical conduction characteristics.
[0036] As explained in more detail below, and as presented in
pending patent application NON-STOICHIOMETRIC SiNxOy OPTICAL
FILTERS, invented by Joshi et al., filed Apr. 26, 2007, Ser. No.
11/789,947, Attorney Docket No. SLA8118, which is incorporated
herein by reference, HDP plasma processed semiconductor
nanoparticles embedded Si insulating thin films show a wide optical
dispersion depending on the processing conditions. It is possible
to vary the refractive index and the extinction constant of the
films. In addition, the HDP plasma process enables the independent
control of the n and k values, which can be successfully exploited
for the fabrication of devices with wide process margins, and a
significant reduction in process complexity and cost.
[0037] The selection of the thin films for optoelectronic
applications depends on the optical, electrical, mechanical, and
chemical properties. The selection of the fabrication technique and
deposition process is equally important for the fabrication of high
quality thin films. Various thin film characteristics such as
microstructure, grain size, composition, density, defects and
impurities, structural homogeneity, and interfacial characteristics
are strongly influenced by the deposition technique and process
parameters.
[0038] As used herein, a nc-Si embedded SiO.sub.xN.sub.y (x+y<2)
thin film is also referred to as a non-stoichiometric
SiO.sub.XN.sub.Y thin-film, where (X+Y<2 and Y>0). A
non-stoichiometric SiO.sub.XN.sub.Y thin-film, as used herein, is
understood to be a film with nanocrystalline (nc) Si particles, and
may also be referred to as a Si-rich SiO.sub.XN.sub.Y thin-film.
The term "non-stoichiometric" as used herein retains the meaning
conventionally understood in the art as a chemical compound with an
elemental composition that cannot be represented by a ratio of
well-defined natural numbers and is, therefore, in violation of the
law of definite proportions. Conventionally, a non-stoichiometric
compound is a solid that is understood to include random defects,
resulting in the deficiency of one element. Since the compound
needs to be overall electrically neutral, the missing atom's charge
requires compensation in the charge for another atom in the
compound, by either changing the oxidation state, or by replacing
it with an atom of a different element with a different charge.
More particularly, the "defect" in a non-stoichiometric
SiO.sub.XN.sub.Y involves nanocrystalline particles.
[0039] The HDP technique is suitable for the fabrication of high
quality thin films due to high plasma density, low plasma
potential, and independent control of plasma energy and density.
The HDP technique is also attractive for the fabrication high
quality films with minimal process or system induced impurity
content. The HDP processed films exhibit superior bulk and
interfacial characteristics due to minimal plasma induced
structural damage and process-induced impurities, as compared to
conventional plasma based deposition techniques such sputtering,
ion beam deposition, capacitively-coupled plasma (CCP) source based
PECVD, and hot-wire CVD. The present invention describes an HDP
process for the creation of nano-semiconductor particles in Si
insulating films in the as-deposited state. The nc-semiconductor
particle concentration can be further enhanced by post-deposition
annealing. The electrical conductivity, photo-response,
photoluminescence (PL), and electroluminescence (EL)
characteristics can be improved by defect passivation treatments.
The HDP processed nc-semiconductor embedded Si insulating films
have tunable optical dispersion characteristics which can be
exploited for the fabrication of optoelectronic devices.
[0040] Another significant aspect of the nc-semiconductor embedded
Si insulating films is significant PL emission in the visible part
of the spectrum, which can be used for the fabrication of active
optical devices exhibiting signal gain and wavelength tuning. The
optical characteristics of the HDP processed thin films can be
further tuned by doping suitable impurities to control the optical
response extending on either side of the visible spectrum, i.e.,
deep UV to far IR. The HDP technique is also suitable for low
temperature and low thermal budget defect passivation of the films
for an enhanced electrical and optical response.
[0041] FIG. 4 is a schematic drawing of a high-density plasma (HDP)
system with an inductively coupled plasma source. The top electrode
1 is driven by a high frequency radio frequency (RF) source 2,
while the bottom electrode 3 is driven by a lower frequency power
source 4. The RF power is coupled to the top electrode 1, from the
high-density inductively coupled plasma (ICP) source 2, through a
matching network 5 and high pass filter 7. The power to the bottom
electrode 3, through a low pass filter 9 and matching transformer
11, can be varied independently of the top electrode 1. The top
electrode power frequency can be in the range of about 13.56 to
about 300 megahertz (MHz) depending on the ICP design. The bottom
electrode power frequency can be varied in the range of about 50
kilohertz (KHz) to about 13.56 MHz, to control the ion energy. The
pressure can be varied up to 500 mTorr. The top electrode power can
be as great as about 10 watts per square-centimeter (W/cm.sup.2),
while the bottom electrode power can be as great as about 3
W/cm.sup.2.
[0042] One interesting feature of the HDP system is that there are
no inductive coils exposed to the plasma, which eliminates any
source-induced impurities. The power to the top and bottom
electrodes can be controlled independently. There is no need to
adjust the system body potential using a variable capacitor, as the
electrodes are not exposed to the plasma. That is, there is no
crosstalk between the top and bottom electrode powers, and the
plasma potential is low, typically less than 20 V. System body
potential is a floating type of potential, dependent on the system
design and the nature of the power coupling.
[0043] The HDP tool is a true high-density plasma process with an
electron concentration of greater than 1.times.10.sup.11 cm.sup.-3,
and the electron temperature is less than 10 eV. There is no need
to maintain a bias differential between the capacitor connected to
the top electrode and the system body, as in many high-density
plasma systems and conventional designs such as
capacitively-coupled plasma tools. Alternately stated, both the top
and bottom electrodes receive RF and low frequency (LF) powers.
[0044] High quality stoichiometric SiO.sub.xN.sub.y (x+y=2) and
nc-Si embedded SiO.sub.xN.sub.y (x+y<2) thin films can be
processed by HDP techniques at process temperatures below
400.degree. C. Some of the substrates that are suitable for
integrated optical devices are Si, Ge, glass, quartz, SiC, GaN,
Si.sub.xGe.sub.1-x. The HDP processed films can be doped in-situ by
adding a dopant source gas or incorporating physical sputtering
source in the chamber along with the high-density PECVD setup. The
optical properties of the HDP processed films can also be modified
by implanting dopant species. Some typical process conditions for
the fabrication of stoichiometric SiO.sub.xN.sub.y (x+y=2) and
nc-Si embedded SiO.sub.xN.sub.y (x+y<2) thin films by HD-PECVD
technique are listed in Table 1.
TABLE-US-00001 TABLE 1 High-density plasma deposition of
stoichiometric SiO.sub.xN.sub.y (x + y = 2) and nc-Si embedded
SiO.sub.xN.sub.y (x + y < 2) thin films Top Electrode Power
13.56-300 MHz, up to 10 W/cm.sup.2, Bottom Electrode Power 50
KHz-13.56 MHz, up to 3 W/cm.sup.2 Pressure 1-500 mTorr Si source
Any suitable Si precursor (SiH.sub.4, Si.sub.2H.sub.6, TEOS, etc.)
e.g.: SiH.sub.4 Oxygen Source Any suitable source of oxygen:
(O.sub.2, O.sub.3, NO, etc.) e.g.: N.sub.2O, O.sub.2 Nitrogen
Source Any suitable source of nitrogen (NH.sub.3, N.sub.2, etc.)
e.g.: N.sub.2 Inert Gases ion the plasma Any suitable inert gas:
Noble gases, N.sub.2, etc. nc-Si particle creation and nc-Si
particles: Silicon source + defect passivation Oxygen source +
inert gases + H.sub.2 Passivation: Source of hydrogen (NH.sub.3,
H.sub.2, etc.) Temperature 25-400.degree. C.
[0045] FIG. 5 depicts a setup used for photo-response measurements.
Photo-response measurements were conducted on nc-Si embedded SiOx
thin films in a MOS-C configuration with transparent ITO as the top
electrode. The light source for the measurements was a probe
station microscope (50.times. objective) and a lamp hanging on the
box. The photo-conduction measurements were performed on three
different square electrodes with side dimensions of 100, 200, and
400 .mu.m. The box light was effective in generating appreciable
charge carriers in the films.
[0046] FIG. 6 is a graph depicting photo-conduction characteristics
of a 200 nm-thick film deposited on an n.sup.+ silicon substrate.
As shown, the reverse leakage current of the film was found to
increase by an order of magnitude as a result of box light
illumination, even though the source was more than 1 m away and the
light was blocked by the objective. When illuminated by the light
through a 50.times. objective, the current was found to increase by
many orders of magnitude. The room temperature SNR ratio was
greater than 1000 at an applied electric field of -500 kV/cm. When
the light was turned off, the leakage current was found to
instantly jump back to the dark current levels.
[0047] FIGS. 7A and 7B are graphs depicting the effect of the film
thickness and Si substrate doping on the photo-response
measurements. The photo-response of 50 nm-thick films, deposited on
n.sup.+ (FIG. 7A) and p.sup.+ (FIG. 7B) Si substrates, was
analyzed. As shown, the 50 nm-thick films exhibit high SNR on both
n.sup.+ and p.sup.+ substrates, exceeding 1000 at an applied
electric field of -500 kV/cm, when illuminated by a light through a
20.times. objective.
[0048] FIGS. 8A and 8B are graphs depicting the effect of
temperature on current using films deposited on an n.sup.+
substrate. The photo-response was analyzed in the range of
25-200.degree. C. for 50 and 200-nm-thick films. For a 50 nm-thick
film, the dark current (FIG. 8A) was found to increase by less than
two orders of magnitude, even at a measurement temperature of
200.degree. C. The increase was found to be lower than a factor of
10, up to a measurement temperature of 100.degree. C. The
ON-current (FIG. 8B) was also found to increase with an increase in
the measurement temperature. However, the increase was within an
order of magnitude, up to a measurement temperature of 200.degree.
C.
[0049] FIG. 9A is a graph depicting SNR for a 50 nm-thick film
deposited on an n.sup.+ silicon substrate. The 50 nm-thick films
show high SNR characteristics with stable dark current
characteristics. The SNR ratio remains higher than 100, even at a
measurement temperature of 200.degree. C. The observed
photo-response of the nc-Si embedded SiO.sub.x thin films offers
significantly enhanced SNR and thermal stability over conventional
Si photodiode based sensors.
[0050] FIGS. 9A and 9B illustrate some optical dispersion
characteristics of nc-Si embedded SiO.sub.x thin films. It is
possible to tune the refractive index and the extinction
coefficient of the films independently. The independent control of
the n and k values enables a better control of the optical
transmission, reflection, and absorption characteristics for the
design of novel optical and optoelectronic devices. The optical
absorption edge of the films can also be effectively controlled by
varying the thin film composition and the nc-Si particle size. The
combination of the n, k dispersion, absorption edge, and PL/EL
emission characteristics can be exploited for the fabrication of
novel optical and optoelectronic devices with controlled optical
response characteristics.
[0051] FIGS. 10A through 10C illustrate the PL spectrum of some HDP
processed nc-Si embedded SiO.sub.x thin films covering the visible
part of the spectrum. The emitted wavelength depends strongly on
the particle size. The HDP plasma process is efficient in the
controlling the particle size over a wide range covering the entire
visible spectrum. The HDP process is effective in the creation of
the nc-Si particles at a low process temperature of 300.degree. C.,
as is evident in the appreciable PL signal. The PL emission
intensity is significantly enhanced by post-deposition annealing
treatment at higher temperatures, which is due to phase separation
and quantum confinement effects. Additionally, the HDP technique is
suitable for the low temperature and low thermal budget defect
passivation.
[0052] To summarize, single or multilayer structures can be made
using the above-described nc-Si embedded SiO.sub.xN.sub.y
(x+y<2) thin films, with control over n, k, and wavelength
emission in terms of film composition, annealing treatment,
passivation, and nc-particle size control. Active waveguides can be
formed capable of wavelength conversion and narrowing down the
wavelength spectrum. Group IV, rare earth dopants can be added to
the films for wavelength control. Optical gain and birefringence
can be exploited for optoelectronic applications. Enhanced optical
emission control over the emitted wavelength can be obtained by
doping. The nc-Si embedded SiO.sub.xN.sub.y (x+y<2) thin films
can be used with a wide range of other materials. For example,
optical wave-guides can be integrated with PIN diode detectors.
Also, nc-Si embedded thin films can be integrated with wide
band-gap semiconductors or phosphors for enhanced light emission
and control. Additional details of the fabrication processes can be
found in a related pending patent application entitled, HIGH
DENSITY PLASMA STOICHIOMETRIC SiOxNy FILMS, invented by Pooran
Joshi et al., Ser. No. 11/698,623, filed on Jan. 26, 2007, Attorney
Docket No. SLA8117, which is incorporated herein by reference.
[0053] FIG. 11 is a flowchart illustrating a method for fabricating
a semiconductor nanoparticle embedded Si insulating film for
photo-detection applications. Although the method is depicted as a
sequence of numbered steps for clarity, the numbering does not
necessarily dictate the order of the steps. It should be understood
that some of these steps may be skipped, performed in parallel, or
performed without the requirement of maintaining a strict order of
sequence. The method starts at Step 1100.
[0054] Step 1102 provides a bottom electrode. Step 1104 introduces
a semiconductor precursor and hydrogen. Step 1105a heats the
substrate to a temperature of less than about 400.degree. C.
Optionally, higher temperatures may be used. Step 1106 deposits a
thin-film overlying the substrate, using a HD PECVD process. In one
aspect, the HD PECVD process uses an inductively coupled plasma
(ICP) source. In another aspect, the HD PECVD process uses a plasma
concentration of greater than 1.times.10.sup.11 cm.sup.-3, with an
electron temperature of less than 10 eV. Step 1108 forms a
semiconductor nanoparticle embedded Si insulating film including
either N or C elements. For example, the semiconductor nanoparticle
embedded Si insulating film may be non-stoichiometric
SiO.sub.XN.sub.Y thin-film, where (X+Y<2 and Y>0). The
optical dispersion characteristics of the non-stoichiometric
SiO.sub.XN.sub.Y thin-film films can also be tailored by varying
the values of X and Y with respect to the thickness of the
thin-film. Alternately, the semiconductor nanoparticle embedded Si
insulating film may be SiC.sub.X, where X<1. The semiconductor
nanoparticles are either Si or Ge.
[0055] In one aspect, supplying the semiconductor precursor and
hydrogen in Step 1104 includes supplying a precursor selected from
a group consisting of Si.sub.nH.sub.2.sub.n+2 and
Ge.sub.nH.sub.2n+2, where n varies from 1 to 4, SiH.sub.xR.sub.4-x
where R is selected from a first group consisting of Cl, Br, and I,
and where x varies from 0 to 3, and GeH.sub.xR.sub.4-x where R is
selected from the first group (Cl, Br, or I), and x varies from 0
to 3.
[0056] In another aspect, supplying the semiconductor precursor and
hydrogen in Step 1104 includes substeps. Step 1104a supplies power
to a top electrode at a frequency in the range of 13.56 to 300
megahertz (MHz), and a power density of less than 10 watts per
square centimeter (W/cm.sup.2). Step 1104b supplies power to a
bottom electrode at a frequency in the range of 50 kilohertz to
13.56 MHz, and a power density of up to 3 W/cm.sup.2. Step 1104c
uses an atmosphere pressure in the range of 1 to 500 mTorr, and
Step 1104d supplies an oxygen source gas. For example, N.sub.2O,
NO, O.sub.2, or O.sub.3 may be used. Then, forming the
semiconductor nanoparticle embedded Si insulating film in Step 1108
includes forming a SiO.sub.XN.sub.Y thin-film. In a different
aspect, Step 1104e supplies an inert noble gas. In another aspect,
Step 1104 supplies a nitrogen source gas such as N.sub.2 or
NH.sub.3.
[0057] Alternately, if Step 1104d supplies Si.sub.nH.sub.2n+2 and a
C source, then Step 1108 forms a SiC.sub.X thin-film. The C source
may be any suitable hydrocarbon-containing precursor. Some examples
of hydrocarbon-containing precursors include alkanes
(C.sub.nH.sub.2n+2), alkenes (C.sub.nH.sub.2n), alkynes
(C.sub.nH.sub.2n-2), Benzene (C.sub.6H.sub.6), and Toluene
(C.sub.7H.sub.8).
[0058] In one aspect, following the formation of the semiconductor
nanoparticle embedded Si insulating film, Step 1110 anneals by
heating the substrate to a temperature of greater than about
400.degree. C., for a time duration in the range of about 10 to 300
minutes, and in an atmosphere including oxygen and hydrogen.
Optionally, the atmosphere may also include inert gases. Then, Step
1112 modifies the size of the semiconductor nanoparticles in the
SiO.sub.XN.sub.Y thin-film in response to the annealing. The
annealing process may use a heat source having a radiation
wavelength in the range of about 150 to 600 nm, or in the range of
about 9 to 11 micrometers.
[0059] In addition to, or as an alternative to the annealing
process, Step 1114 performs a HD plasma treatment with the
semiconductor nanoparticle embedded Si insulating film in an
H.sub.2 atmosphere, using a substrate temperature of less than
400.degree. C. Step 1116 hydrogenates the semiconductor
nanoparticle embedded Si insulating film.
[0060] More particularly, Step 1116 may include the following
substeps. Step 1116a supplies power to a top electrode at a
frequency in the range of 13.56 to 300 MHz, and a power density of
up to 10 W/cm.sup.2. Step 1116b supplies power to a bottom
electrode at a frequency in the range of 50 kilohertz to 13.56 MHz,
and a power density of up to 3 W/cm.sup.2. Step 1116c uses an
atmosphere pressure in the range of 1 to 500 mTorr, and Step 1116d
supplies H.sub.2 and an inert gas.
[0061] In a different aspect, Step 1109 optionally dopes the
semiconductor nanoparticle embedded Si insulating film with a Type
3, Type 4, Type 5, or rare earth element dopant prior to a phase
separation anneal in Step 1110. Alternately, Step 1113 dopes the
semiconductor nanoparticle embedded Si insulating film after the
phase separation annealing of Step 1110. The doping step can be
executed before or after annealing. Annealing is typically required
after doping to activate the dopants. Overall, annealing has two
purposes: (1) to induce phase separation, and (2) activate the
dopants. In response to doping, Step 1108 forms a semiconductor
nanoparticle embedded Si insulating film with (modified) optical
absorption or emission characteristics in the range of frequencies
from deep ultraviolet (UV) to far infrared (IR). As noted above,
the doping may be performed in-situ using a dopant source gas or
physical sputtering source.
[0062] In addition to, or as an alternative to annealing, following
the formation of the SiO.sub.XN.sub.Y thin-film, Step 1120 oxidizes
the non-stoichiometric SiO.sub.XN.sub.Y thin-film using either a
plasma or thermal oxidation process. Then, Step 1122 modifies the
size of semiconductor nanoparticles in the SiO.sub.XN.sub.Y
thin-film in response to the oxidation process.
[0063] Photodetectors have been described that are made with
semiconductor nanoparticles embedded Si insulating films. Specific
examples of SiO.sub.X1N.sub.Y1 thin-films and SiO.sub.X1N.sub.Y1
thin-film fabrication details have been presented. Some details of
other specific materials and process details have also been used to
illustrate the invention. However, the invention is not limited to
merely these examples. Other variations and embodiments of the
invention will occur to those skilled in the art.
* * * * *